Today's display glass substrates are delivered to customers with minimal treatment, or sometimes no treatment at all. Most of the glass substrates are cut to size and are then washed using an aqueous surfactant solution. This solution is designed to help remove glass and abrasive particles that are deposited on the glass surface during the cutting and edge grinding of the glass. Such washing does not offer any further benefit to thin-film transistors (“TFTs”).
Metallic impurities at or within the top surface layer of a glass substrate can degrade the performance of thin film transistors (TFTs) and other electronic devices fabricated on the substrate. For example, metallic impurities present at the glass/semiconductor interface can cause an increase in the leakage current between the source and drain electrodes. If metallic impurities become incorporated into the semiconductor film at levels close to the designed free carrier concentration, reduced gate control may occur, as well as an increase in current leakage and other erratic operation characteristics. The concentration of these metallic impurities exceeding the designed free carrier concentration may lead to complete device failure due to an open circuit or short circuit condition. Metallic impurities contaminating the gate insulator can also lead to erratic threshold voltage variation and/or premature dielectric breakdown and destruction of the transistor.